As an example of a mixer circuit according to the conventional art, JP-A-2004-357091 discloses a Gilbert cell type double balanced mixer circuit shown in FIG. 16 (see FIG. 10 of JP-A-2004-357091). In the Gilbert cell type double balanced mixer circuit, one differential amplification transistor pair MB and MC is connected in series to a circuit where two differential switch transistor pairs MD and ME and MF and MG are cross-connected. Herein, the MA is a current source transistor for bias. Loads 111 and 112 are connected to a supply voltage VDD. A differential radio frequency signal RF inputs RF+ and RF− is amplified by a differential amplification transistor pair and an output of the amplified differential radio frequency signal and a frequency signal LO input from a local oscillator mounted on a receiver are multiplied by the differential switch transistor pair, such that a differential intermediate frequency signal IF (IF+ and IF−) is output and amplified to be an output signal having an amplitude larger than that of an input signal.
John R. Long et al, “A 1.9 GHz Low-Voltage Silicon Bipolar Receiver Front-End for Wireless Personal Communications Systems”, IEEE Journal of Solid-State circuits, Vol. 30, No. 12, pp. 1438-1448, December 1995, discloses a mixer circuit that includes a single-to-differential converter using a transformer T1 as shown in FIG. 17 (see FIG. 9 of John R. Long et al). A radio frequency signal RFin is single-to-differential converted by the transformer T1 and is frequency-converted via differential switch transistor pairs Q1 and Q2 and Q3 and Q4, such that intermediate frequency signals IF+ and IF− are output. Q5 is a current source transistor for bias. The single-to-differential conversion can be performed by this configuration. Q6 and Q7 are a Darlington buffer.
Further, JP-A-2004-357091 discloses a mixer circuit using a wideband balun shown in FIG. 18 (see FIG. 2 of JP-A-2004-357091) in order to solve problems of the mixer circuit in the conventional art shown in FIG. 16. The mixer circuit includes a low-noise amplifier LNA 121 that includes an amplifier stage transistor M1, a cascode stage transistor M2, and a load 124 and amplifies an RF signal (radio frequency signal), a balun 122 that converts an RF signal (single end signal) from the LNA 121 into a differential signal, and a switch circuit 123 that mixes a differential signal from the balun with a local originating signal LO. The RF signal (radio frequency signal) is supplied to the gate of the amplifier stage transistor M1 together with a bias voltage supplied through a resistor 125.